Technical Field
This invention relates generally to methods and apparatus for physical rehabilitation through exercise, such as devices that exercise those muscles which power and articulate the ankles and more particularly such devices wherein the user's movements are opposed by a selected resistance.
Background of the Invention
Often athletes and many non-athletes utilize weight lifting or weight training exercises to build muscle strength, to prevent injury, or to improve overall condition and appearance. Typically, weight training exercises are performed with either exercise machines or free weights, such as barbells with weighted plates or dumbbells. Exercise machines in general are adapted to provide resistance for specific upper or lower body movements, but none no prior art exercise machines are adapted to provide resistance for the normal range of ankle movements.
Gait parameters, static balance and dynamic stability tend to deteriorate as we age. While there are sensory factors contributing to the loss, a primary cause is the regression of ankle strength and flexibility. This loss of strength and flexibility causes a strategy shift in stability control among the elderly, moving away from foot and ankle control towards hip movements for maintaining balance and dynamic stability. This change is not widely appreciated, except by professionals involved in rehabilitation training, and the degree of change will vary in individual's cases. Through experience, physical therapists have developed various floor exercises for addressing the need which, while helpful, are limited in scope and cannot provide the significant benefits of progressive resistance training.
Certain weight resistance machines, specifically calf raise machines and leg press machines, do provide linear, unidirectional weight training for the legs and ankles. A traditional calf raise machine provides sagittal plane resistance training for the ankle joint. The prime mover or “agonist” is the muscle group responsible for joint action during an exercise. The muscles acting at the ankles during a calf raise exercise are the plantarflexors, while all other muscles surrounding the joint are essentially uninvolved. However, the muscular responses needed to maintain stability must act in planes throughout 360° around the ankles. Complex muscle groups act to flex the ankles as required for maintaining stability. These ankle flexions or movements are briefly described as aversion or inversion in combination with plantar or dorsal flexion.
Plantarflexion is movement of the ankle which increases the angle between the tibia bone (shin) and top of the foot, giving the appearance of pointing the toes. Dorsiflexion is movement of the ankle which decreases the angle between the shin and the top of the foot, bringing the top of the foot closer to the shin. Inversion is turning the ankle and foot inward, which would give the appearance of putting the soles of the feet together. Eversion is turning the ankle and foot outward.
The first muscle group acts for inversion:                The tibialis anterior acts for inversion and dorsiflexion.        The tibialis Posterior acts for inversion and plantarflexion.        The flexor digitorum longus acts for inversion and plantarflexion.        The soleus and gastrocnemius act for plantarflexion.        
The second muscle group acts for aversion:                The extensor digitorum longus acts for aversion and dorsiflexion.        The peroneus longus acts for aversion and plantarflexion.        The peroneus brevis acts for aversion and plantarflexion.        
It is noteworthy that, aside from the soleus and gastrocnemius, which act solely for plantarflexion, the other ankle muscle groups have compound, bidirectional functionality. To varying degrees maintaining stability involves every one of the above muscles, according to the direction in which stability is challenged. Forward stability is maintained by plantarflexors responses and rearward stability is maintained by an opposite dorsiflexor response. Lateral stability is maintained by invertor/evertor muscle group responses. Since these muscles act together in diverse harmony, they exemplify muscle groups which cannot be effectively exercised and developed by movements confined to a single plane. While there are helpful floor exercises, calf raise and leg press machines, the provision of progressive bidirectional resistance training for these muscle groups is unknown to the prior art.
A skilled physical therapist might manipulate the foot and ankle through an appropriate range of motion, so as to improve flexibility, but without resistance there can be no beneficial strengthening. In order to provide some strengthening, the therapist might enforce ankle inversion accompanied by plantarflexion against the patient's resistance and then ankle aversion accompanied by dorsiflexion. However, if it were possible to provide resistance to such movements according to a progressive weight training program, the associated muscles could be strengthened to a degree not possible with prior art methodology and equipment.
Therefore, an object of the present invention is to provide apparatus for bi-directional ankle exercises, where movements are not confined to a single plane or direction. A second object is to provide apparatus for implementing the manual method of rehabilitation therapy. A third object is to provide resistance for these bi-directional movements according to a progressive weight training program. Yet a further object is that such apparatus be suitable for professionally unsupervised use in a gymnasium or home environment.